Relative similarity and classification of layer 3 pyramidal neurons in mouse and rhesus monkey frontal and visual cortices. (A) Discriminant analyses cluster plot showing grouping of individual cells into the 4 groups of neurons based on intrinsic passive and firing electrophysiological properties (canonical correlation, r: discriminant function df₁ = 0.8, df₂ = 0.65, df₃ = 0.61; Wilks' λ: test of function 1–3 = 0.12, 2–3 = 0.37, 3 = 0.63, P < 0.001), sEPSC properties (r: df₁ = 0.79, df₂ = 0.52; Wilks' λ: 1–3 = 0.27, 2–3 = 0.73, P < 0.001), dendritic topology (r: df₁ = 0.995, df₂ = 0.79, df₃ = 0.65; Wilks' λ: 1–3 = 0.002, 2–3 = 0.22, 3 = 0.58, P < 0.023) and spine distribution (r: df₁ = 0.89, df₂ = 0.7; Wilks' λ: 1–2 = 0.11, 2 = 0.5, P < 0.001). (B) Hierarchical cluster and discriminant analyses based on all electrophysiological and morphological variables combined: hierarchical cluster tree showing the relative (dis)similarities of the 4 groups of neurons and discriminant analysis plot showing clustering of individual cells (r: df₁= 1, function df₂ = 0.97; Wilks' λ: 1–2 < 0.001, P < 0.0001; 2 = 0.057, P < 0.057).